Cups of artificial cardiac valve and method for manufacturing thereof

ABSTRACT

The invention relates to medical technology and could be used in manufacturing artificial cardiac valves having one or more cusps made of a polymer composite. The method for manufacturing a cusp of an artificial cardiac valve, includes the steps of: manufacturing a casting mold, and molding a cusp from a polymer composite comprising 78 to 92% by weight of polyamide and 8 to 22% by weight of radiographic contrast medium dispersed therein. The polymer composite can comprise additionally fine acetylene black in amount of 1 to 2% by weight. The preferred radiographic contrast medium is barium sulphate. In one embodiment of the method, the casting mold is manufactured for the molding size 1 to 5% less than necessary, and the cusp is placed after molding into an anticoagulant solution and matured therein until expanding by 1 to 5%.

REFERENCES TO RELATED APPLICATIONS

This patent application is a US National Phase of PCT-RU2006-000601based on a Russian Federation patent application RU2006126142, herebyentirely incorporated by reference.

FIELD OF THE INVENTION

The invention relates to medical technology and could be used inmanufacturing artificial cardiac valves.

BACKGROUND OF THE INVENTION

Artificial cardiac valves can comprise one, two, or more cusps havingpaired protrusions for fastening in the valve casing. During the valveoperation, the protrusions experience a maximal mechanical loading.

Known is the method for manufacturing a cusp for an artificial cardiacvalve made of titanium alloy with a coating made of pyrocarbon (RUPatent No. 2012284, 1994). However, the cusp made of two-layer materialdoes not possess sufficient reliability when operating continuously fora long period of time. Moreover, in mounting the cusp protrusions insockets of the casing, metal-to-metal friction problems arise.

Also known is a method for manufacturing the cusp by producing thepyrocarbon layer of controllable thickness on the surface of a graphitesubstrate by means of: deposing it, when decomposing carbon compoundsfrom a gaseous stream in a through-flow reactor; separating subsequentlythe pyrocarbon layer from the substrate; and further processingmechanically pyrocarbon in order for shaping thereof in the form of acardiac valve cusp (U.S. Pat. No. 6,274,191, 2001). The disadvantages ofthe method are its long duration, labor intensity, and the mechanicalprocessing being performed manually, particularly at the final stage.

Known are methods for manufacturing the valve cusps from materials madeon a polymer base. According to SU Inventor Certificate No. 1144216,1987, cusps are manufactured of organic-silicon rubber reinforced bythreads made of the same material. The RU Patents Nos. 2057494, 1996 and2153887, 2000, describe methods for manufacturing cusps from polyesterurethane. In the first instant, the cusp material includes additionallyreinforcing fabric. In the second instance, the method provides formodifying the cusp surface using the pulse plasma spraying of carbon.

All the described methods are time-consuming and expensive, and thematerial of the cusps made by such methods does not keep mechanicalproperties and hemo-compatibility for a long time, as well as does notpermit for checking for a condition of the artificial cardiac valvewithout surgical intervention.

BRIEF DESCRIPTION OF THE INVENTION

The claimed invention enables to simplify and cheapen significantly theprocess for manufacturing the cusps, increase hemo-compatibility andreliability of the artificial cardiac valve in the most loaded loci, aswell as enables to observe the cusp operation in X-rays.

The method for manufacturing a cusp of an artificial cardiac valveincludes the steps of: manufacturing a casting mold, and subsequentlymolding a cusp from a polymer composite comprising 78 to 92% by weightof polyamide and 8 to 22% by weight of radiographic contrast mediumdispersed therein.

Additionally, the polymer composite could comprise fine acetylene blackin an amount of 1 to 2% by weight. The presence of the black in thecomposite polymer permits to enhance the tribo-technical characteristicsof the artificial cardiac valve, especially in long-term operationthereof.

Preferably, barium sulphate (BaSO₄) serves as the radiographic contrastmedium. However, this function could be performed by other materials:bismuth oxychloride (BiOCl), bismuth oxide (Bi₂O₃), basic bismuthcarbonate (BiO)₂CO₃, etc. In the case, when the composite formulationcomprises less than 8% of the radiographic contrast medium, monitoringthe cusp operation in X-rays becomes substantially impossible. Whenthere is more than 22% of the radiographic contrast medium, the cuspmaterial resistance to alternating loads reduces to unacceptable levelin a long-term operation.

Experience has shown that the polymer composite used for manufacturingthe cusps of artificial cardiac valves can expand during a long-termcontact with liquids, particularly blood. In this case, the cusps of theartificial cardiac valve expands in size by 1 to 5%. Such an increase insize could result in disturbances of the cusp operation and even inimpaction thereof.

In order for preventing such cases, the mold for casting the cusp ismanufactured for the molding size 1 to 5% less than necessary, and,after the molding step, the cusp is placed into an anticoagulant (e.g.,heparin) solution and matured therein until expanding by 1 to 5%. Thus,a double result is achieved: ensuring the cusp size stability during along-term operation, and reducing a thrombosis probability in contactingblood with the material of the artificial cardiac valve.

EXAMPLES OF IMPLEMENTATION OF THE INVENTIVE METHOD Example 1

An initial mixture for manufacturing the cusps of an artificial cardiacvalve was prepared for loading into a molding machine. The mixture wasprepared by combined grinding and stirring thoroughly at the same timean 86% weight portion of polyamide and a 14% weight portion of bariumsulphate. The resulted mixture was loaded into a heatable cylinder ofthe molding machine and heated up to 230° C. The hot melt wassupercharged into the casting mold, whose surface temperature was 75° C.After 15 sec of solidification, the casting mold was opened, and theformed cusp molding was pushed out onto a soft substrate in conditionsof the room temperature and normal atmospheric pressure. When thecasting mold has been made thoroughly, the produced cusp required noadditional size perfection and surface processing (finishing).

The cusps thus produced (without taking into account a possiblesubsequent expansion) are mated for each annular valve casing takinginto account a dimensional tolerance in manufacturing thereof, in orderfor excluding an excessively tight fit of the cusp in the casing andpossible impaction of the valve in case of the cusp expansion.

Example 2

The initial mixture was prepared similarly to the one in the previousexample, but with addition of acetylene black. The mixture for thepolymer composite comprised 80% by weight of polyamide, 18% by weight ofbarium sulphate, and 2% by weight of acetylene black. The casting moldwas made for the molding size 2% less than necessary. The temperature ofmixture prior to the supercharging into the casting mold was 240° C.,the temperature of the casting mold surface was 80° C. After thesolidification, the valve cusp was pushed out of the casting mold into aheparin solution heated to 38° C. and matured therein for 3 hours forexpanding (swelling). The produced cusp required no additionalprocessing prior to mounting into the casing of the artificial cardiacvalve.

Producing the valve cusps by the method of casting from a polymercomposite permits to sharply increase the productivity and reduce theprocessing cost for manufacturing the artificial cardiac valves.

1. A method for manufacturing a cusp of an artificial cardiac valve,including the steps of: manufacturing a casting mold, and molding a cuspfrom a polymer composite comprising 78 to 92% by weight of polyamide and8 to 22% by weight of radiographic contrast medium dispersed therein;wherein the polymer composite additionally comprises fine acetyleneblack in the amount of 1 to 2% by weight.
 2. A method for manufacturinga cusp of an artificial cardiac valve, including the steps of:manufacturing a casting mold, and molding a cusp from a polymercomposite comprising 78 to 92% by weight of polyamide and 8 to 22% byweight of radiographic contrast medium dispersed therein; wherein thecasting mold is manufactured for the molding size of from 1 to 5% lessthan necessary, and, after the step of molding, the cusp is placed intoan anticoagulant solution and matured therein until expanding by from 1to 5%.
 3. A cusp of an artificial cardiac valve made of a polymermaterial, characterized in that the cusp is made from a polymercomposite comprising from 78 to 92% by weight of polyamide and from 8 to22% by weight of radiographic contrast medium dispersed therein, whereinthe polymer composite additionally comprises fine acetylene black in theamount of 1 to 2% by weight.